Honest or play it cool... salvaging a missed connection?

I met a great girl a couple years ago at a dinner. We talked all night and I walked her home. I screwed up by not asking her for her number or if she'd want to go out some time. She seemed really surprised when I said nice to meet you and left, so I think she may have liked me as well.

Two years later, and I still regret that decision. Maybe I should just move on, but I can't shake the feeling that there might have been something there. We became fb friends after the dinner, and she invited me to a party she was hosting last year, so I guess she still remembers me too, no idea in what sense though.

I want to reach back out to her some way. My first idea if to invite her to a party early in the year and see if she shows up, which would make it easy to talk to her, catch up a bit, and gauge he interest.

If she doesn't come to that though, I still want to reach out, which would have to be over fb bc thats the only way I have to get in touch. Here lies the question. After two years and having never talked online, how the heck do I approach that conversation. It feels random to just say "Hey, how's life" out of the blue, but it seems way to forward to tell her the truth of how I feel. Where is the middle ground, and how do I approach it?